Add diagnostic code pages to documentation

[joshuadavidthomas]

This came up in #339 but the diagnostic codes are not documented anywhere, you have to look in the source to see them:

django-language-server/crates/djls-ide/src/diagnostics.rs

Lines 70 to 81 in d5d43ad

	fn diagnostic_code(&self) -> &'static str {
	match self {
	ValidationError::UnclosedTag { .. } => "S100",
	ValidationError::UnbalancedStructure { .. } => "S101",
	ValidationError::OrphanedTag { .. } => "S102",
	ValidationError::UnmatchedBlockName { .. } => "S103",
	ValidationError::MissingRequiredArguments { .. }
	| ValidationError::MissingArgument { .. } => "S104",
	ValidationError::TooManyArguments { .. } => "S105",
	ValidationError::InvalidLiteralArgument { .. } => "S106",
	ValidationError::InvalidArgumentChoice { .. } => "S107",
	}

There should be either a page with all of them listed (like djlint has for it's codes), or maybe like ruff a dedicated page for each code. Dedicated pages would be a bit more work, but probably worth it in the long run? Linkability and being able to provide examples -- though I suppose you could achieve that with a single page too, so 🤷.

[joshuadavidthomas]

Added some basic documentation in #347, but I do think dedicated pages for these would be nice -- so examples of the errors and how to fix them could be included.